This invention relates to a fixing device of an electrophotographic copying apparatus and the like comprising a heating roller and a pressure applying roller forming a pair and maintained in rolling contact with each other to allow a toner image bearing recording sheet to pass therebetween to fix the toner image on the recording sheet.
A fixing device of the aforesaid type has been known and used widely with various types of recording apparatus including electrophotographic copying apparatus, printers, electrostatic recording apparatus, etc. In this type of fixing device, a toner image is fixed to a recording sheet mainly by the action of heat. As a result, elements of the fixing device, particularly the heating roller, are heated to a high temperature. If heating of the elements of the fixing device is left to run its course, the heat of the fixing device would be transferred to other devices of the recording apparatus and might exert injurous influences thereon. Particularly in a recording apparatus of the type in which the operator has the risk of touching the fixing device or devices located in the vicinity of the fixing device due to their structural relation, the accident of the operator having his or her hand burned by the heat of the heated fixing device might happen.
To avoid such accident, proposals have hitherto been made to surround the elements of the fixing device by a heat insulating material layer. However, the provision of a single heat insulating layer has been unable to achieve the desired results when the fixing device is operated for a prolonged period of time because the heat insulating layer is heated and its outer surface becomes very high in temperature. To avoid this trouble, proposals have been made to use a fan for blowing air toward the outer surface of the heat insulating material layer to lower the temperature of the outer surface thereof. However, the use of a fan has had the effect of scattering the heated air to the vicinity of the fixing device, thereby adversely affecting the devices in the vicinity of the fixing device.
In one type of fixing device, when a recording sheet passed between the heating roller and pressure applying roller adheres to the heating roller, the recording sheet is stripped off the heating roller by at least one stripping claw member in contact with the too heating roller. It is difficult, however, to avoid the trouble of a recording sheet jamming as the result of it being bitten by the heating roller and the forward end of the stripping claw member in this type of fixing device. This makes it nececessary to provide the fixing device with means for readily removing the recording sheet when jamming of the recording sheet occurs. Various proposals have been made and carried into practice to provide means for avoiding the occurrence of a recording sheet jam. For example, in one proposal, means is provided for moving the stripping claw member away from the feating roller together with elements located in its neighborhood to remove from between the heating roller and the stripping claw member moving away therefrom the recording sheet that has been stuck between the heating roller and the stripping claw member. When the stripping claw member is moved away from the heating roller, a sharp forward end of the stripping claw member is exposed from the fixing device to outside. Thus, there is the risk of the operator being injured when his hand inadvertently comes into contact with the forward end of the stripping claw member in removing the recording sheet stuck between the heating roller and the stripping claw member. To avoid this trouble, it is known to let the forward end of the stripping claw member remain facing downwardly without being exposed to outside when the stripping claw member is moved away from the heating roller. This type of fixing device of the prior art has suffered the disadvantge of being complex in construction and high in cost. A proposal has been made to move the stripping claw member away from the heating roller together with a heat insulating cover when a recording sheet jam occurs. However, it is impossible to obviate the aforesaid disadvantage by carrying this proposal into practice. Besides being unable to avoid the aforesaid disadvantage, moving the heat insulating cover away from the heating roller or opening the heat insulating cover exposes the heating roller to outside, with a result that the hand of the operator might be inadvertently brought into contact with the heating roller and suffer burns. Also, when the aforesaid proposal of moving the stripping claw member away from the heating roller together with elements located in its vicinity when a recording sheet jam occurs is carried into practice, it would be necessary to locally cut a large portion of the heat insulating cover to avoid the trouble of the heat insulating cover being interfered with by the retreating stripping claw member. However, this would result in a marked reduction in the effects achieved by the heat insulating cover in insulating heat.